The objective of this research program is to further our understanding of how genetic, environmental, and physiological (hormonal and neural) variables act and interact to produce differences in behavior. The experimental subjects are laboratory mice (Mus musculus). The behavior under study is the masculine sexual response pattern of this species. Current research is concerned primarily with four different preparations: normal male mice; castrated-copulating male mice; castrated-noncopulating male mice; and neonatally-androgenized (NA) female mice. Possible studies include: (1) Does the direct relationship between androgen level and ejaculation latency in B6D2F1 castrated males hold for other genotypes and for NA females within this species? (2) Response of castrated males and NA females to aromatizable and nonaromatizable androgens and estrogen in adulthood. (3) What is the role of the adrenal glands during the difficult period following castration in B6D2F1 male mice? (4) Is response to castration related to endogenous hormone level prior to castration? (5) Radioimmunoassay of plasma testosterone levels.